1. Technical Field of the Invention
The present invention relates to a method for characterizing the moment at which a bit is detected within an electronic circuit. It also relates to a circuit that incorporates a binary data receiver together with a test module for this receiver.
2. Description of Related Art
When an integrated electronic circuit that incorporates a binary data receiver is fabricated, the operation of the latter needs to be verified for each circuit unit produced. In particular, it needs to be verified that the data transmitted to the receiver is correctly detected. This is notably the case when the data is received according to the HDMI (High-Definition Multimedia Interface) standard.
Now, the moment of detection of a bit received can vary within a read period of the bit, notably because of external interference. Such variations are capable of causing a bit detection error. For this reason, the statistical distribution of the detection times within successive read periods must be determined during circuit operational tests.
In order to perform these tests, a specific module is added to the integrated electronic circuit, which is often called BIST (Built-In Self-Test) module. Although not usable during the circuit operation according to the function for which the circuit is designed, this module nevertheless results in a cost increase for the circuit. It is therefore advantageous to design a simple BIST module, and notably a BIST module that occupies as small an electronic circuit substrate surface area as possible.
The test of each circuit unit produced is carried out using a specific monitoring instrument, called a tester, whose price varies considerably depending on the technical requirements demanded of the tester. For example, a tester that operates at a rate of 320 Mbit/s has a much lower cost than a tester which operates at a rate of 1.6 Gbit/s. In fact, the demands on the performance of the tester depend on the functions performed within the BIST module, which is why a compromise is sought between a simplified BIST module and the necessity for using a costly tester.
In order to determine the statistical distribution of bit detection times situated within successive read periods, each read period needs to be sub-divided in the same manner into elementary time intervals, and the number of times where a bit is detected within each sub-division interval needs to be counted. However, a system rate that corresponds to the elementary intervals of time from the sub-division will be high. In order to avoid using a tester that operates at such a high rate, a known solution is to create these elementary intervals by using two frequencies separated by a small difference, for timing the read periods and for triggering the bit detection, respectively. Thus, the tester generates a bit detection trigger signal at a first frequency, and generates a binary signal at a second, slightly different, frequency. The signal at the second frequency is synthesized within the tester starting from the signal at the first frequency, with a high enough precision to define the elementary time intervals for the read period sub-division by the progressive shift which occurs between the two signals. The signal at the second frequency corresponds to the bits detected by the circuit receiver during the test.
However, counting the number of times where a bit is detected within each sub-division elementary time interval requires that the bit be transmitted a given number of times, for example 256 times, whereas the detection is sought within a given elementary interval. The same operation must then be repeated for each elementary interval. The result of this is a long test duration, which contributes to an increase in the production cost of each electronic circuit unit produced.
There is a need in the art to be able to characterize the statistical distribution of the bit detection times, while achieving an improved compromise between a simplified BIST module, on the one hand, a tester that is not too costly, on the other, and furthermore providing a test of limited duration.